Field of the Invention
The present invention relates to a method for manufacturing an oxide semiconductor, and more particularly to a crystallization method for an oxide semiconductor layer, which achieves an enhancement in crystallization characteristics, thereby achieving an enhancement in reliability of the resultant device, a semiconductor device manufactured using the same, and a method for manufacturing the semiconductor device.
Discussion of the Related Art
With the advent of the information age, the demand for various display devices has increased. To meet such a demand, efforts have recently been made to research display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), electroluminescent display (ELD) devices, vacuum fluorescent display (VFD) devices, and the like. Some types of such display devices are being practically applied to various appliances for display purposes.
Such a display device includes a thin film transistor (TFT) array substrate including thin film transistors (TFTs) formed at respective pixel areas as switching elements. The TFTs are formed at respective pixel areas defined through intersection of gate lines and data lines. Each TFT is formed with an active layer to form a channel area, a gate insulating film, a gate electrode, a source electrode and a drain electrode.
In conventional cases, the active layer is made of silicon. In particular, crystalline silicon has been required to obtain sufficient carrier mobility and stable electrostatic characteristics. For such crystallization, however, high temperature of 500° C. or more is required. In order to withstand such a high temperature process, there is a limitation in selection of a support substrate formed with an active layer. For this reason, use of the above-mentioned material in a flexible substrate may be impractical.
Recently, transparent oxide semiconductors have been highlighted and, as such, attempts to apply the material to an active layer have been made.
Japanese Patent Publication No. JP2011-100979 discloses crystallization of a surface of an active layer in a semiconductor device in order to achieve contact characteristics of the active layer with respect to source/drain electrodes disposed thereon while preventing permeation of moisture into the surface of the active layer when an oxide semiconductor is applied to the active layer of the semiconductor device. Japanese Patent Publication No. JP2011-146697 discloses crystallization of an oxide semiconductor layer through heat treatment carried out several times at 650° C. or more after deposition of the oxide semiconductor layer. The former discloses crystallization of only the surface of the oxide semiconductor layer, and the latter discloses formation of a double layer structure including a semiconductor layer as a first layer and an oxide semiconductor layer as a second layer, and utilization of the first layer, namely, the semiconductor layer, as a seed for formation of crystals.
In the above-mentioned oxide semiconductor crystallization methods, however, high temperature of 500° C. or more is required as a heat treatment temperature in application of the above-mentioned silicon crystallization. For this reason, it may be difficult to stably maintain the support substrate, which exhibits low heat resistance, during a crystallization process. As a result, it may be difficult to use the above-mentioned methods in manufacture of a large-area display device.